The present invention relates to a method of stuffer box crimping a multifilament yarn, as well as an apparatus for carrying out the method.
To produce a crimped yarn, it is known to compress a freshly spun yarn consisting of a plurality of filaments to a yarn plug by means of a crimping device. To this end, the crimping device is designed and constructed, for example, as a texturing nozzle. This texturing nozzle comprises a yarn channel, in which a hot medium, preferably air advances the yarn. The yarn channel terminates in a stuffer chamber. The yarn plug is formed inside the stuffer chamber. In this process, the yarn deposits in loops on the surface of the yarn plug and is compressed by the conveying medium, which is allowed to escape from the stuffer chamber through slots above the yarn plug. Subsequently, the yarn plug is removed from the stuffer chamber and cooled by means of a downstream cooling device. After cooling, the yarn plug is unraveled to the crimped yarn.
In this process, the crimp of the yarn is decisively influenced in its intensity and stability by the plug formation and by the thermal treatment of the yarn plug. Thus, besides the temperature and the pressure of the conveying medium, the dwelling time of the yarn plug during the thermal treatment also constitutes a parameter that has a decisive influence on the crimping result.
For example, it has been known for a long time to control the feed and/or the withdrawal speed of the yarn such that a uniform formation of the yarn plug is maintained during the process. An apparatus and a method of this kind are disclosed, for example, in DE 1 236 126. There, for purposes of monitoring the yarn plug, the position of the unraveling point at the end of the yarn plug is determined and adjusted to a predetermined level by changing the withdrawal speed of the yarn.
The known method is suitable only to a limited extent to produce a yarn with a uniform crimp, since it does not enable a direct intervention in the formation of the yarn plug. Thus, for example, fluctuations in the temperature or the pressure of the conveying medium may lead to considerable differences in the crimp of the yarn.
To be able to intervene in the thermal treatment of the yarn directly, DE 23 24 827 proposes a method and an apparatus, wherein the heat supply to the yarn plug is adjusted as a function of the position of the unraveling point of the yarn plug.
Furthermore, it is known from DE 42 24 454 and related U.S. Pat. No. 5,088,168 to adjust the heat supply to the yarn plug as a function of a yarn tension necessary to unravel the yarn plug.
The known methods, wherein the heat supply is adjusted to realize a uniform crimp in the yarn, are unsuitable in processes operating at high yarn speeds of more than 3,000 m/min. The intervention in the yarn plug formation is too sluggish to prevent the yarn plugs from shifting, which leads to an unsteady behavior of the process in the extreme case.
It is therefore an object of the invention to provide a method of stuffer box crimping a multifilament yarn of the initially described kind, as well as an apparatus for carrying out the method, wherein a yarn is produced with a uniform crimp in particular at high yarn speeds of more than 3,000 m/min.